Washington: Amid a raging political storm back home, Pakistan's envoy to the US Husain Haqqani has left for Islamabad, where he would explain his position with regard to the controversy over a secret memorandum in which his country's civilian leadership purportedly sought American help to stave off a possible military takeover.

Before leaving for Islamabad, Haqqani met Special US Representative for Af-Pak region Marc Grossman at the State Department and the issue of the memo is believed to have been discussed.

"On way to motherland Pakistan," Haqqani tweeted on Friday night after his meeting with Grossman.

The Pakistani Ambassador had offered to resign after a secret memo purportedly written by him on behalf of President Asif Ali Zardari was delivered to Admiral Mike Mullen, the then Chairman of the Joint Chiefs of Staff, by an eminent Pakistani-American businessman, days after Osama bin Laden was killed in a US raid in Abbottabad.

Haqqani has strongly denied that he had anything do with that memo, which is now doing the rounds of the media domain.In the secret memo, Zardari purportedly sought Mullen's assistance against a possible military takeover and talked about creating a new national security team.

After initial reluctance, Mullen has acknowledged having received such a memo, but says he did not act on it and did not take it seriously.

Pentagon Press Secretary George Little on Friday told reporters Defence Secretary Leon Panetta is aware of the issues related to the memo.

However, he said that "no review" has been ordered when asked why the serious allegations in the memo were ignored by the office of the Chairman of the Joint Chiefs of Staff.

Meanwhile, the State Department termed the issue as an internal matter of Pakistan and refrained from making any comment on it.

"I understand this is a big story in Pakistan. It's partly a domestic story. We all treat it as such. We remain in contact with Ambassador Haqqani," State Department spokesman Mark Toner said.

"Our understanding is that he (Haqqani) is still the Ambassador of Pakistan to the United States, and we continue to have regular interactions with him, as we do with a number of people both within the Pakistani government," Toner said in response to a question.

Haqqani on Friday met Grossman, during which it is believed that the issue of memo did come up.

No readout of the meeting was immediately available. Grossman said that he had not seen the memo until it became public.

Pakistan's ruling PPP on Friday decided that Haqqani would be given a "fair opportunity" to explain his position with regard to the controversy over the secret memorandum.

Separately, Premier Yousuf Raza Gilani denied Zardari's involvement in the matter and also said his government was committed to protecting military institutions like ISI.

He said Haqqani had been called to Islamabad to provide an explanation on the memorandum.